The purpose of this study is to provide a comprehensive analysis of risk factors for the development of clinical cardiotoxicities in over 6,000 children with cancer who have been treated on standardized protocols involving the use of anthracyclines alone or in combination with other potentially cardiotoxic therapies or with no use of anthracycline therapy. The data will be analyzed to estimate the incidence of clinical cardiotoxicity as measured by sudden death, congestive heart failure, or discontinuation of therapy based on cardiac function. Evaluation of patient characteristics (age, anemia) and treatment factors such as drug, dose level, dosing schedule, exposure to irradiation and/or cyclophosphamide will identify groups at particularly high risk for development of clinical cardiotoxicity and provide estimates of this risk for future treatment planning. Such estimates of high risk groups will make possible future trials to test the feasibility of using cardioprotectors or alternate dosing schedules to prevent cardiotoxicity. The incidence of clinical cardiotoxicity will be calculated using Kaplan- Meier estimates as a function of total cumulative anthracycline dose and also as a function of the time since the end of treatment stratified by dose levels. The estimates will be stratified by exposure to cyclophosphamide and radiation therapy. Multivariate methods will be used to evaluate the prognostic significance of selected patient characteristics and treatment parameters and to provide estimates of the relative risk of each variable. The method of recursive partitioning will be used to identify subpopulations at elevated risk for clinical cardiotoxicity. The data and analytic techniques are accessible through SAS data sets and procedures available to the study at the Pediatric Oncology Group (POG) Statistical Office.